Method and apparatus for dot matrix writing using a continous wave laser

Abstract

A method and apparatus for writing bits (or pixels) on a target by scanning a continuous wave laser beam across an array of concave mirrors. The radiation reflected from the concave mirror array images a row of stationary dots on the target during each scan. To write a dot matrix pattern, after each row of dots is written on the target, the target is translated (perpendicularly to the row of dots) by an increment, and another row of dots is then written on the target. The laser beam can be modulated while it is scanned across the concave mirror array, for example, by being selectively transmitted through a shutter. Preferably, the beam is swept across the concave mirror array by reflecting from a rotating mirror (which can be flat or polygonal with multiple facets). In a class of preferred embodiments of the invention, lines of variable length and width (rather than dots) are written on the target. This is accomplished by scanning the continuous wave laser beam across a system of variable lenses. The scan is accomplished by reflecting the beam from a rotating mirror, so that a swept beam transmitted through the lens system is projected as a line on the target.

What is claimed is: 
     
       1. An apparatus for marking a target by exposing the target to continuous wave laser radiation, including: a means for generating a continuous wave laser beam;   an array of concave mirrors;   a means for scanning the continuous wave laser beam across the array, wherein said means for scanning includes a rotating mirror, and said means for scanning includes a means for reflecting the laser beam from the rotating mirror;   a target positioned relative to the array so that each concave mirror in the array projects a stationary real image of the laser beam on the target when the laser beam is scanned across the array, wherein the stationary real image is projected on the target for a dwell time determined by a rotational velocity of the rotating mirror; and   control means, connected to the means for scanning, for controlling the rotational velocity to control the dwell time.   
     
     
       2. The apparatus of claim 1, also including: laser beam modulation means for modulating the laser beam before said laser beam is scanned across the array of concave mirrors.   
     
     
       3. The apparatus of claim 2, wherein the laser beam modulation means is a shutter device. 
     
     
       4. The apparatus of claim 2, wherein the laser beam modulation means is an acousto-optic modulator. 
     
     
       5. The apparatus of claim 1, also including: control means, connected to the means for generating the continuous wave laser beam, for supplying control signals to said means for generating the continuous wave laser beam to terminate generation of the laser beam at desired times.   
     
     
       6. The apparatus of claim 1, also including: control means, connected to the means for generating the continuous wave laser beam, for supplying control signals to said means for generating the continuous wave laser beam to modulate generation of the laser beam at desired times.   
     
     
       7. The apparatus of claim 1, wherein the concave mirrors in the array are oriented so that they project a row of stationary dots on the target. 
     
     
       8. The apparatus of claim 7, wherein the row is oriented in a first direction, and also including means for: translating the target in a second direction substantially perpendicular to the first direction.   
     
     
       9. The apparatus of claim 1, wherein the rotating mirror is a rotating flat mirror. 
     
     
       10. The apparatus of claim 1, wherein the rotating mirror is a rotating polygonal mirror having reflective facets, and wherein the array of concave mirrors is positioned relative to the rotating polygonal mirror so that radiation reflected from each of the facets scans across the array of concave mirrors as the polygonal mirror rotates. 
     
     
       11. The apparatus of claim 10, also including a secondary array of mirrors positioned so that the radiation reflected from each of the facets re-reflects from the secondary array of mirrors, and the re-reflected radiation then scans at least twice across the array of concave mirrors as the polygonal mirror rotates. 
     
     
       12. The apparatus of claim 1, also including: a lens system for focusing radiation reflected from the array, wherein the lens system has a magnification selected so that the real image of the laser beam projected on the target has a desired size.   
     
     
       13. The apparatus of claim 1, also including: means for collimating radiation that has reflected from the array, before said radiation is projected on the target.   
     
     
       14. The apparatus of claim 1, wherein the array of concave mirrors includes individual concave mirrors that are mounted adjacent to each other, with a minimal separation between each pair of adjacent ones of the concave mirrors. 
     
     
       15. The apparatus of claim 1, wherein the array of concave mirrors is a mirror member having a concave front surface consisting of concave reflective portions, wherein the reflective portions are separated by substantially parallel grooves extending through said concave front surface, and wherein the mirror member also includes a flexible back portion through which no grooves extend. 
     
     
       16. An apparatus for marking a target by exposing the target to continuous wave laser radiation, including: a means for generating a continuous wave laser beam;   an optical element;   a rotating mirror;   a means for projecting the laser beam onto a first point which coincides with a surface of the rotating mirror to produce a reflected beam which propagates away from the rotating mirror, and for scanning the reflected beam across the optical element to produce an output beam which forms a real image of the first point at a stationary image point, wherein a cross-section of the output beam near the real image moves only a short distance during a dwell time, determined by a rotational velocity of the rotating mirror, which can be made sufficiently long to directly mark the target without need for a light sensitive surface or photographic process;   a target positioned relative to the optical element in such a position that the optical element projects a line of laser radiation on the target for said dwell time when the reflected beam is scanned across the optical element; and   control means, connected to the rotating mirror, for controlling the rotational velocity to control the dwell time.   
     
     
       17. The apparatus of claim 16, wherein the optical element is a lens system. 
     
     
       18. The apparatus of claim 17, wherein the line has a width, wherein the lens system includes a lens that is translatably mounted along an optical axis between the rotating mirror and said means for generating the continuous wave laser beam, and wherein translation of the lens along the optical axis controls the width of the line. 
     
     
       19. The apparatus of claim 17, wherein the line has a length, wherein the lens system includes a lens mounted along an optical axis between the rotating mirror and the target, and wherein translation of the lens along the optical axis controls the length of the line. 
     
     
       20. The apparatus of claim 16, also including: control means for controlling operation of the means for generating the continuous wave laser beam, wherein the control means includes ceases generation of the laser beam at desired times.   
     
     
       21. The apparatus of claim 16, wherein the rotating mirror is a rotating polygonal mirror having reflective facets. 
     
     
       22. A system for directly marking information on a target surface in a pattern of dots, wherein the dots are arranged to form columns of dot matrix alpha-numeric characters, including: a laser which emits a beam of radiation;   means for moving the target surface relative to the laser in a direction substantially perpendicular to the columns;   means for modulating the beam to mark on the target surface, or omit, individual ones of the dots selectively to generate alpha-numeric characters, wherein a projection of the beam at each of the dots remains stationary for a dwell time which can be made sufficiently long to directly mark the target surface without need for a light sensitive surface or photographic process;   means for scanning the beam from a rotating polygonal mirror having facets and an angular velocity, across an array of concave spherical mirrors, so that reflection of the beam from said concave spherical mirrors produces a real image, on the target surface for each of the dots, of a point at which the beam is incident on one of the facets; and   means for controlling the dwell time for marking each of the dots on the target surface to match characteristics of said target surface, by varying the angular velocity.   
     
     
       23. The system of claim 22, wherein the laser is an R.F. excited carbon dioxide, and the means for modulating the beam includes means for modulating the beam by directly modulating an R.F. signal supplied to the laser. 
     
     
       24. The system of claim 22, wherein the array of concave spherical mirrors is adjustable to control separation between adjacent ones of the dots in each of the columns. 
     
     
       25. A system for directly marking information on a target surface in a pattern of lines, wherein the lines are arranged to form columns of dot matrix alpha-numeric characters, including: a laser which emits a beam of radiation;   means for moving the target surface relative to the laser in a direction substantially perpendicular to the columns;   means for modulating a beam of radiation emitted by the laser to selectively mark full lines or shortened lines on the target surface, or omit individual ones of the lines, thereby generating the alpha-numeric characters;   means for scanning the beam from a rotating polygonal mirror having facets and an angular velocity, across a lens system, so that the beam transmitted through the lens system produces a real image of a point at which the beam is incident on one of the facets, wherein a cross-section of the beam near the real image moves only a short distance during a dwell time which can be made sufficiently long to directly mark the target surface without need for a light sensitive surface or photographic process; and   means for controlling the dwell time for marking each of the lines on the target surface to match characteristics of said target surface, by varying the angular velocity.   
     
     
       26. The system of claim 25, wherein the laser is an R.F. excited carbon dioxide, and the means for modulating the beam includes means for modulating the beam by directly modulating an R.F. signal supplied to the laser. 
     
     
       27. The system of claim 25, wherein each of the full lines has a length less than fifteen millimeters. 
     
     
       28. The system of claim 25, wherein the lens system includes a lens translatably mounted along an optical axis between the rotating polygonal mirror and the laser. 
     
     
       29. The system of claim 25, wherein the lens system includes a lens translatably mounted along an optical axis between the rotating polygonal mirror and the target surface. 
     
     
       30. A system for directly marking information on a target surface in a pattern of lines, wherein the lines are arranged in columns, including: a laser which emits a beam of radiation; means for moving the target surface relative to the laser in a direction substantially perpendicular to the columns;   means for modulating a beam of radiation emitted by the laser to selectively mark full lines or shortened lines on the target surface, or omit individual ones of the lines, thereby generating selected arrangements of lines;   means for scanning the beam from a rotating polygonal mirror having facets and an angular velocity, across an optical element, so that the optical element produces a real image of a point at which the beam is incident on one of the facets, wherein a cross-section of the beam near the real image moves only a short distance during a dwell time which can be made sufficiently long to directly mark the target surface without need for a light sensitive surface or photographic process; and   means for controlling the dwell time for marking each of the lines on the target surface to match characteristics of said target surface, by varying the angular velocity.   
     
     
       31. A mirror member for use in a laser writing apparatus, including: a front portion consisting of concave portions, wherein the concave portions are separated by substantially parallel grooves extending through said front portion; and   a flexible back portion through which no grooves extend.   
     
     
       32. The mirror member of claim 31, also including: a reflective coating on each of the concave portions.   
     
     
       33. The mirror member of claim 32, wherein the reflective coating is composed of gold, and wherein the front portion and the flexible back portion are composed of copper. 
     
     
       34. A method for marking a target by exposing the target to continuous wave laser radiation, including the steps of: (a) scanning a continuous wave laser beam across an array of concave mirrors, by reflecting the laser beam from a rotating mirror;   (b) positioning the target relative to the array so that, during step (a), each concave mirror in the array projects a stationary real image of the laser beam on the target, wherein the stationary real image is projected on the target for a dwell time determined by a rotational velocity of the rotating mirror, and also including the step of:   controlling the rotational velocity to control the dwell time.   
     
     
       35. The method of claim 34, also including the step of: (c) modulating the laser beam before scanning said laser beam across the array of concave mirrors.   
     
     
       36. The method of claim 35, wherein step (c) includes the step of selectively transmitting the laser beam through a shutter device. 
     
     
       37. The method of claim 35, also including the step of operating a laser to generate the laser beam, and wherein step (c) includes the step of controlling operation of the laser so as to cease generation of the laser beam at desired times. 
     
     
       38. The method of claim 34, wherein the concave mirrors in the array are oriented so that they project a row of stationary dots on the target during step (a). 
     
     
       39. The method of claim 38, wherein the row is oriented in a first direction, and also including the steps of: (c) after step (b), translating the target in a second direction substantially perpendicular to the first direction; and   (d) after step (c), repeating steps (a) and (b).   
     
     
       40. The method of claim 38, wherein the row is oriented in a first direction, and also including the steps of: (c) after step (b), translating the target in a second direction substantially perpendicular to the first direction;   (d) after step (c), preventing the laser beam from scanning across the array for a selected period of time; and   (e) after step (d), repeating steps (a) and (b).   
     
     
       41. The method of claim 34, wherein the rotating mirror is a rotating flat mirror. 
     
     
       42. The method of claim 34, wherein the rotating mirror is a rotating polygonal mirror having reflective facets, and wherein radiation reflected from each of the facets scans across the array of concave mirrors as the polygonal mirror rotates. 
     
     
       43. The method of claim 42, wherein the radiation reflected from each of the facets re-reflects from a secondary array of mirrors, and then scans at least twice across the array of concave mirrors as the polygonal mirror rotates. 
     
     
       44. The method of claim 34, also including the step of focusing radiation reflected from the array through a lens system, wherein the lens system has a magnification selected so that the real image of the laser beam projected on the target has a desired size. 
     
     
       45. The method of claim 34, also including the step of collimating radiation that has reflected from the array, before projecting the radiation on the target. 
     
     
       46. The method of claim 34, wherein the array of concave mirrors includes individual concave mirrors that are mounted adjacent to each other, and wherein there is a minimal separation between each pair of adjacent concave mirrors. 
     
     
       47. The method of claim 34, wherein the array of concave mirrors is a mirror member having a concave front surface consisting of reflective portions, wherein the reflective portions are separated by substantially parallel grooves extending through the concave front surface, and wherein the mirror member also includes a flexible back portion through which no grooves extend, and including the step of: bending the back portion of the mirror member so as to orient the reflective portions into a position in which they project a row of stationary dots on the target with a desired inter-dot spacing.   
     
     
       48. A method for marking a target by exposing the target to continuous wave laser radiation, including the steps of: (a) projecting a continuous wave laser beam onto a first point which coincides with a surface of a rotating mirror to produce a reflected beam which propagates away from the rotating mirror;   (b) during step (a), scanning the reflected beam across an optical element to produce an output beam which forms a real image of the first point at a stationary image point, wherein a cross-section of the output beam near the real image moves only a short distance during a dwell time, determined by a rotational velocity of the rotating mirror, which can be made sufficiently long to directly mark the target without need for a light sensitive surface or photographic process; and   (c) positioning the target relative to the optical element so that, during step (b), the optical element projects a line of laser radiation on the target, wherein the optical element projects the line on the target for said dwell time, and also including the step of:   controlling the rotational velocity to control the dwell time.   
     
     
       49. The method of claim 48, also including the steps of: operating a laser to generate the laser beam; and   controlling operation of the laser so as to cease generation of the laser beam at desired times.   
     
     
       50. The method of claim 48, wherein the line of laser radiation is oriented in a first direction, and also including the steps of: (d) after step (c), translating the target in a second direction substantially perpendicular to the first direction; and   (e) after step (d), repeating steps (a), (b) and (c).   
     
     
       51. The method of claim 48, wherein the optical element is a lens system. 
     
     
       52. The method of claim 51, wherein the lens system includes a lens mounted along an optical axis between the rotating mirror and a source of said laser beam, and wherein the line has a width, and including the step of: translating the lens along the optical axis to control the width of the line.   
     
     
       53. The method of claim 51, wherein the lens system includes a lens mounted along an optical axis between the rotating mirror and the target, and wherein the line has a length, and including the step of: translating the lens along the optical axis to control the length of the line.   
     
     
       54. The method of claim 51, wherein the rotating mirror is a rotating polygonal mirror having reflective facets, and wherein a reflected beam from each of the facets scans across the lens system as the polygonal mirror rotates. 
     
     
       55. The method of claim 48, wherein the rotating mirror is a rotating flat mirror. 
     
     
       56. A method for marking a target by exposing the target to continuous wave laser radiation, including the steps of: (a) projecting a continuous wave laser beam onto a first point which coincides with a surface of a rotating polygonal mirror having reflective facets to produce a reflected beam which propagates away from the rotating polygonal mirror;   (b) during step (a), scanning the reflected beam across a lens system to produce an output beam which forms a real image of the first point at a stationary image point, where the stationary image point is a first distance from said lens system, and wherein a reflected beam from each of the facets scans across the lens system as the polygonal mirror rotates; and   (c) positioning the target a second distance away from the lens system so that, during step (b), the lens system projects a line of laser radiation on the target, wherein the difference between the first distance and the second distance is much shorter than the first distance, wherein each said reflected beam is re-reflected from a secondary array of mirrors, and then scans at least twice across the lens system as the polygonal mirror rotates.   
     
     
       57. A method for marking a target by exposing the target to continuous wave laser radiation, including the steps of: (a) projecting a continuous wave laser beam onto a first point which coincides with a surface of a rotating mirror to produce a reflected beam which propagates away from the rotating mirror;   (b) during step (a), scanning the reflected beam across a lens system to produce an output beam which forms a real image of the first point at a stationary image point, where the stationary image point is a first distance from said lens system; and   (c) positioning the target a second distance away from the lens system so that, during step (b), the lens system projects a line of laser radiation on the target, wherein the difference between the first distance and the second distance is much shorter than the first distance, wherein the lens system projects the line on the target for a dwell time determined by a rotational velocity of the rotating mirror, and also including the step of:   controlling the rotational velocity to control the dwell time.   
     
     
       58. A method for directly marking information on a target surface in a pattern of dots using a laser, wherein the dots are arranged in columns to form dot matrix alpha-numeric characters and the target surface moves in a direction substantially perpendicular to the columns, the method including the steps of: (a) scanning the beam from a rotating polygonal mirror having facets and an angular velocity, across an array of concave spherical mirrors, so that reflection of the beam from said concave spherical mirrors projects a real image, on the target surface for each of the dots, of a point at which the beam is incident on one of the facets;   (b) while performing step (a), modulating a beam of radiation emitted by the laser to mark on the target surface, or omit, individual ones of the dots selectively to generate alpha-numeric characters, wherein a projection of the beam at each of the dots remains stationary for a dwell time which can be made sufficiently long to directly mark the target surface without need for a light sensitive surface or photographic process; and   (c) controlling the dwell time for marking each of the dots on the target surface to match characteristics of said target surface, by varying the angular velocity.   
     
     
       59. The method of claim 58, wherein the laser is an R.F. excited carbon dioxide, and step (b) includes the step of modulating the beam by directly modulating an R.F. signal supplied to the laser. 
     
     
       60. The method of claim 58, wherein the laser is an R.F. excited carbon dioxide, and step (b) includes the step of transmitting the beam through a shutter device. 
     
     
       61. The method of claim 58, wherein the array of concave spherical mirrors is adjustable to control separation between adjacent ones of the dots in each of the columns, and also including the step of: adjusting said array of concave spherical mirrors to control separation between said adjacent ones of the dots.   
     
     
       62. The method of claim 58, wherein each of the facets produces one scan across the array of concave spherical mirrors corresponding to marking of one of the columns, and also including the step of: turning off the laser during unwanted scan periods to adjust width of the marked characters.   
     
     
       63. The method of claim 58, wherein each of the facets produces one scan across the array of concave spherical mirrors corresponding to marking of one of the columns, and also including the step of: adjusting the angular velocity to match perpendicular movement of the target surface, so as to adjust width of the marked characters.   
     
     
       64. A method for directly marking information on a target surface in a pattern of dots using a laser, wherein the dots are arranged in columns and the target surface moves in a direction substantially perpendicular to the columns, the method including the steps of: (a) scanning the beam from a rotating polygonal mirror having facets and an angular velocity, across an optical element, so that the optical element projects a real image, on the target surface for each of the dots, of a point at which the beam is incident on one of the facets;   (b) while performing step (a), modulating a beam of radiation emitted by the laser to mark on the target surface, or omit, individual ones of the dots selectively to generate selected arrangements of dots, wherein a projection of the beam at each of the dots remains stationary for a dwell time which can be made sufficiently long to directly mark the target surface without need for a light sensitive surface or photographic process; and   (c) controlling the dwell time for marking each of the dots on the target surface to match characteristics of said target surface, by varying the angular velocity.   
     
     
       65. A system for directly marking information on a target surface in a pattern of dots, wherein the dots are arranged in columns, including: a laser which emits a beam of radiation;   means for moving the target surface relative to the laser in a direction substantially perpendicular to the columns;   means for modulating the beam to mark on the target surface, or omit, individual ones of the dots selectively to generate selected arrangements of dots, wherein a projection of the beam at each of the dots remains stationary for a dwell time which can be made sufficiently long to directly mark the target surface without need for a light sensitive surface or photographic process;   means for scanning the beam from a rotating polygonal mirror having facets and an angular velocity, across an optical element, so that the optical element projects a real image, on the target surface for each of the dots, of a point at which the beam is incident on one of the facets; and   means for controlling the dwell time for marking each of the dots on the target surface to match characteristics of said target surface, by varying the angular velocity.   
     
     
       66. A method for directly marking information on a target surface in a pattern of lines using a laser, wherein the lines are arranged to form columns of dot matrix alpha-numeric characters and the target surface moves in a direction substantially perpendicular to the columns, the method including the steps of: (a) modulating a beam of radiation emitted by the laser to selectively mark full lines or shortened lines on the target surface, or omit individual ones of the lines, thereby generating the alpha-numeric characters;   (b) while performing step (a), scanning the beam from a rotating polygonal mirror having facets and an angular velocity, across a lens system, so that the beam transmitted through the lens system produces a real image of a point at which the beam is incident on one of the facets, wherein a cross-section of the beam near the real image moves only a short distance during a dwell time which can be made sufficiently long to directly mark the target surface without need for a light sensitive surface or photographic process; and   (c) controlling the dwell time for marking each of the lines on the target surface to match characteristics of said target surface, by varying the angular velocity.   
     
     
       67. The method of claim 66, wherein each of the full lines has a length less than fifteen millimeters. 
     
     
       68. The method of claim 66, wherein the laser is an R.F. excited carbon dioxide, and step (a) includes the step of modulating the beam by directly modulating an R.F. signal supplied to the laser. 
     
     
       69. The method of claim 66, wherein the laser is an R.F. excited carbon dioxide, and step (a) includes the step of transmitting the beam through a shutter device. 
     
     
       70. The method of claim 66, wherein the lens system includes a lens translatably mounted along an optical axis between the rotating polygonal mirror and the laser, including the step of: translating said lens along the optical axis to change width of the lines marked on the target surface.   
     
     
       71. The method of claim 66, wherein the lens system includes a lens translatably mounted along an optical axis between the rotating polygonal mirror and the target surface, including the step of: translating said lens along the optical axis to change character height by changing maximum length of a column.   
     
     
       72. The method of claim 66, wherein each of the facets produces one scan across the lens system corresponding to marking of one of the columns, and also including the step of: turning off the laser during unwanted scan periods to adjust width of the marked characters.   
     
     
       73. The method of claim 66, wherein each of the facets produces one scan across the lens system corresponding to marking of one of the columns, and also including the step of: adjusting the angular velocity to match perpendicular movement of the target surface, so as to adjust width of the marked characters.   
     
     
       74. A method for directly marking information on a target surface in a pattern of lines using a laser, wherein the lines are arranged in columns and the target surface moves in a direction substantially perpendicular to the columns, the method including the steps of: (a) modulating a beam of radiation emitted by the laser to selectively mark full lines or shortened lines on the target surface, or omit individual ones of the lines, thereby generating selected arrangements of lines;   (b) while performing step (a), scanning the beam from a rotating polygonal mirror having facets and an angular velocity, across an optical element, so that the optical element produces a real image of a point at which the beam is incident on one of the facets, wherein a cross-section of the beam near the real image moves only a short distance during a dwell time which can be made sufficiently long to directly mark the target surface without need for a light sensitive surface or photographic process; and   (c) controlling the dwell time for marking each of the lines on the target surface to match characteristics of said target surface, by varying the angular velocity.